Cdi performance

[Frankenstein]

I thought about ramping the piston, but won't this affect squish, quench, etc? I think the piston top acts as part of the chamber, would changing the shape change the swirl? Someone please enlighten me on this.

Yes, ramps affect the squish and to a certain extent change the swirl, and can even enhance the swirl.

The top of the piston is absolutely part of the combustion chamber, and it's the part that's most likely to melt under extreme heat, hence the benefits of a squish band.

 

[Deleted member 12676]

yes it affects it, to a huge amount of about 2% !!!

 

[Frankenstein]

yes it affects it, to a huge amount of about 2% !!!

I'll take your statistical word for it..

I do wonder how 2% was chosen since a single ramp covers more than 2% of the piston head surface area, let alone 3...

Just kidding, the actual effect in my opinion wouldn't be much on the actual squish, a small variance in height likely has no real measure able effect on the way a squish works, in fact a ramp introduces new cool fuel and air sooner (by a fraction of a split second, but it exists nonetheless) and allows hot burning fuel to exit earlier than on a standard piston, thereby technically adding to the cooling power of a squish.

Then that just gets canceled out by higher rpm and more heat build up. Almost seems pointless to take the effort of you're going to burn the s**t out of it at 12k rpm or whatever by changing the timing...

Happy time motors, let's not get too excited or technical about them, the point is to be cheap easy fun, not rocket science.

 

[Purple Haze]

Thanks for the replies, guys! I think I was seduced by the "if the port is more open, it'll run better" I also considered cutting the piston skirt to match the transfers, but reason overcame dream. I should know better, as a former car guy, changing anything from stock can make for a temperamental beast (or dog) I'm looking mainly at low-end torque and max fuel economy. Was mainly worried about flame travel and burn time, don't want most of my mixture going out the exhaust port unburned. I did polish the piston top and the chamber to prevent hot spots, I'll leave it at that for now. Jag, you mentioned having the transfer ports equalized on your mods page (lots of good info there) is that the height of the port, and how's the best way to achieve this? Thanks again for all the tips.